The present invention relates to cryosurgical probes, and in particular to a cryoprobe system utilizing a passive, insulated, hand-held thermal mass having a low temperature tip for cryosurgical medical applications and the like, as well as a heat extraction base configured to interface with the thermal mass to quickly and efficiently reduce the heat of the thermal mass to cryogenic temperatures.
The heat extraction base of the preferred embodiment of the present invention is configured to interface with the tip of the thermal mass, such that the tip plugs in securely to the base, to permit an efficient thermal transfer of heat from the thermal mass through the base via a heat exchange system communicating with the base which employs a low temperature cryo-refrigeration unit.
The cryo-refrigeration unit may comprise a single low temperature compressor to reduce the temperature of the base to around minus one hundred degrees Centigrade utilizing off-the-shelf cryogenic refrigeration methods, or may utilize a series of more conventional refrigeration units in a primary and secondary heat extraction arrangement, which method may further utilize thermocouple or Peltier effect device assist to further reduce the temperature of the heat extraction base to the required temperature.
The thermal mass is configured to be cooled to an optimal temperature for cryogenic applications, removed from the base, the tip of the otherwise insulated thermal mass then applied to the surface to be treated, typically tissue on a patient, wherein the cooled thermal mass provides a heat sink via the tip to cryogenically cool the treated surface.
Cryosurgery, or cryo-ablation, employs the technique of destructively freezing, or ablating, targeted biological tissue to destroy same. A large array of systems for cryosurgery have been developed since its inception utilizing low and high pressure cryogenic liquid refrigerants, closed refrigeration systems, to solid state thermoelectric devices.
By far the most common method of performing cryosurgery involves the utilization of fluids having a low boiling point, either applied directly to the tissue of the patient or utilized to cool a probe or applicator tip. Liquid Nitrogen, Nitrous Oxide, Carbon Dioxide, or aerosol (Histofreezer) comprise the most widely used cryosurgical modalities currently in use of this type.
Liquid nitrogen has been widely utilized for cryosurgery since the 1940""s, when it became more readily available. In low pressure applications, typically a Dewar-type storage flask is required to store the liquid, which must be replenished on a regular basis. The physician may spray the liquid on the tissue to be applied, or may dip a cotton swab or the like into the liquid nitrogen to absorb said liquid, thereafter applying the swab to the portion to be treated.
While Liquid Nitrogen has a boiling point of xe2x88x92196 degrees Centigrade, when employed in cryosurgery, erratic temperatures can arise. For example, when dabbed on with a cotton swab, skin surface temperatures can be as high as xe2x88x920 degrees Centigrade, but can go as low as xe2x88x92100 degrees Centigrade if a continuous flow of LN2 is applied to the skin rapidly.
Alternatively, a probe having a tip configured to conform to the anatomy to be applied may be chilled to cryogenic temperatures by the liquid, flowing therethrough, and allowing same to boil to adsorb heat, allowing the tip to act as a heat sink. Utilization of such a probe is preferred in gynecologic, oral, rectal, or other invasive applications, where the probe can be formed to conform with the anatomy to which it is applied. As the evaporation of the fluid is the principle behind its cooling properties, an emission of the gas occurs in the area in which it is employed.
Nonetheless, liquid Nitrogen provides the most effective, widely utilized cryogen fluid, having a low boiling point of xe2x88x92196 degrees Centigrade. This low temperature in and of itself provides risks, due to possible over application and associated over freezing, as well as risks of spills, and possible splattering during handling, as even indirect contact to tissue can result in tissue damage. Protective eyewear, clothing, and gloves are therefore required, and the material must be stored and administered under Federal OSHA guidelines.
Nitrous Oxide and Carbon Dioxide are similarly used, but are stored in a pressurized tanks, so they have the benefit of not being depleted during storage. However, studies have shown that Nitrous Oxide can be harmful to a Fetus, and breathing Nitrous Oxide can result in reduced fertility in females. Further, liquid Nitrous Oxide boils at a higher temperature (xe2x88x9289 degrees Centigrade) than Nitrogen, which can result in a less effective treatment. Carbon dioxide when evaporated displaces oxygen in the treatment area, and has even a higher boiler point (xe2x88x9278 degrees Centigrade) than Nitrous Oxide, which makes it far less suitable as a refrigerant. Nitrous oxide can employ a J-T expansion tip to reach tip temperatures down to about xe2x88x9289 degrees centigrade, and is favored as a reliable temperature delivery system, but suffers as its downside the above mentioned health risks.
HISTOFREEZE is a liquid refrigerant formulation comprising an aerosol which may be dispensed to a cotton swab or other application tip via an aerosol can. However, the refrigerant has a much higher boiling point than nitrogen, resulting in less cooling to the tissue (about xe2x88x922 degrees Centigrade) to be treated, and is thereby far less effective. Like the above refrigerants, the aerosol evaporates into the atmosphere of the treatment area which can be breathed by its occupants, unless it is vented.
The liquid nature of the above refrigerants makes it very difficult to precisely cool the treated area to an exact temperature, resulting in the tissue often being undercooled or overcooled. While the degree of cooling varies with the type of tissue and depth and type of abnormality, the area should generally be exposed to at least xe2x88x9220 degrees Centigrade, and ideally xe2x88x9250 degrees centigrade to effectively treat malignant tissue.
In addition to the above methods, cryosurgical treatment devices utilizing self contained cooling apparatus have also been employed, but these units have often proved expensive, cumbersome and difficult to use, while rarely providing the cooling effectiveness of liquid nitrogen. Accordingly, such devices have not been employed in any significant extent compared with the above systems.
A list of patents which may have some pertinence to the present invention include:
U.S. Pat. No. 5,132,089 to Lightfoot teaches a xe2x80x9cHand-Held Cryofixation Apparatusxe2x80x9d wherein xe2x80x9ca metal block is precooled by immersion into a cryogen such as liquid nitrogen or helium.xe2x80x9d
U.S. Pat. No. 4,037,631 to Schulze et al teaches a xe2x80x9cMethod of Charging a Cryogenic Probexe2x80x9d wherein a probe is inserted in a cryogenic liquid container (FIG. 4-7).
U.S. Pat. Nos. 3,502,080 and 4,519,389 teach diverse cryogen probes having application tips which are cooled via thermocouple or Peltier effect devices.
U.S. Pat. No. 3,668,888 teaches a xe2x80x9cdevice for frosting drinking glassesxe2x80x9d wherein heat is extracted from a glass via a cooling device which releases refrigerant into the glass to evaporatively cool same.
U.S. Pat. No. 3,451,395 to Thyberg teaches a cryosurgical instrument wherein the probe tip is cooled via cryogenic fluid, which is allowed to boil in the tip via an air vent, so as to extract heat from the tip to cryogenically cool same.
U.S. Pat. No. 3,575,176 teaches a xe2x80x9cRechargeable Cryosurgical Instrumentxe2x80x9d having a refrigerant receiving chamber, and a tip which would receive the refrigerant, which tip would be exposed to the atmosphere to allow evaporation of the refrigerant so as to cool same. See also U.S. Pat. No. 3,451,395 for a device of similar operation but different configuration.
U.S. Pat. No. 6,096,032 issued Aug. 1, 2000 teaches a xe2x80x9cMicro Cryo-Surgical Devicexe2x80x9d wherein there is provided a thermoelectric device configured to engage and remove heat from a brass cooling block, the block mounted on to the neck of a Dewar flask containing a coolant, illustrated as a ethylene glycol/water mixture. The cooling block has passages formed therethrough for the passage of the coolant, wherein heat is extracted from same via the thermoelectric device; the coolant is then directed to a second thermoelectric device which interfaces with a copper application tip. The second thermoelectric device, with heat extracted by the coolant, further cools the copper application tip so that it may be utilized in cryogenic surgery applications.
It is anticipated that the ""032 device, utilizing conventional thermoelectric devices, would be incapable of extracting sufficient heat from the application tip to provide the heat removal necessary for most cryogenic surgery applications.
Thus, there would appear that the prior art has yet failed to provide a cryogenic device which does not require the use of liquid nitrogen or the like, and instead relying upon closed refrigeration cycles to develop sufficient heat removal from the application tip in an relatively cost effective, easily implemented, and reliable fashion.
Unlike the prior art, the present invention is believed to provide a system and method for cryosurgery which is safe to use, reliable in operation, cost effective to implement and maintain, and straightforward in use.
In cryosurgery treatment of diseased tissues, the most critical factor is the safe, controlled, freezing of the tissue to the desired, acceptable tissue range. To date the prior art has provide systems wherein it is difficult to gauge the effective freezing of diseased tissues; too often the tissues are overcooled, destroying surrounding tissues, or undercooled, resulting in ineffective treatment. Cell destruction typically starts at about xe2x88x9210 degrees Centigrade to xe2x88x9220 degrees Centigrade, but usually xe2x88x9240 degrees Centigrade to xe2x88x9250 degrees Centigrade is preferable, as this better assures cell destruction.
The preferred embodiment of the present invention comprises two primary components, a hand-held cryogen applicator, comprising an insulated thermal mass having an exposed end which is configured to engage an application tip, and a thermal cooling unit which includes a base having a socket configured to engage said exposed end of the thermal mass, so as to remove heat from said thermal mass to cool same to cryogenic temperatures.
The first working embodiment of the present invention utilizes first and second, cascaded Rankine-cycle cooling systems, driven by a motor-compressor to extract heat from a cold plate by circulating coolant therethrough; further, a thermoelectric device (TMD) is sandwiched between the cooling unit base and the cold plate, with the cold side engaging the base, such that heat extracted from said base, and through said TMD via said cold plate, to bring the temperature down still further. A self-filling solution of antifreeze liquid in the form of purified ethanol alcohol is provided in the socket so as to facilitate more efficient removal of heat from the application tip and thermal mass, as well as displace air and the moisture present therein. A working prototype of this system has successfully chilled the thermal mass and application tip to about xe2x88x92100 degrees Centigrade.
The super-cooled thermal mass can then be removed from the thermal cooling unit, fitted with an application tip to the exposed end, and be utilized as a heat sink to cryogenically cool (i.e., remove heat from), via the application tip, the selected tissue.
In the working prototype of the present invention, there are three different sized cryogen applicators, comprising different sized thermal masses, a smaller unit for treating smaller tissue areas such as moles or the like, a medium sized unit, and a larger mass unit, which provides greater heat sink capability, as may be required for larger or more intense applications, such as may be required in gynecological treatments.
The larger the area, the lower the temperature of the tissue that can be achieved, assuming a specific starting temperature. A numeric temperature display is preferably provided on each cryogen applicator so as to accurately and readily indicate to the user the operational condition of the unit in real time. In the first working prototype, the thermal cooling unit included three sockets to simultaneously engage three cryogen applicators, which can be of similar or disparate sizes; when one applicator in use falls below its optimal temperature range, the tip may be removed, the unit plugged into a socket of the thermal cooling for heat removal, and another cryogen applicator removed from one of the other sockets, which applicator has been sufficiently cooled for immediate use.
An alternative embodiment of the present invention utilizes a Stirling-type refrigerant compressor utilizing helium as the refrigerant, which unit may be as small as a soda can, to quickly, efficiently, and quietly form the cooling means for the thermal cooling unit. This alternative unit dispenses with the need of the cascaded, conventional refrigeration systems and thermoelectric device secondary cooler, and provides a smaller, albeit more expensive, footprint than the present working embodiment of the invention.
It is reiterated that the cooling mechanisms employed in the thermal cooler component of the invention can vary from the above, and may further include liquid nitrogen cooling of the cold plate, magnetic coolers, ultrasonic or laser cooling apparatus, diverse evaporative cooling systems, high grade Peltier effect coolers (which may be stacked).
The thermal mass forming the thermal application of the first working prototype comprised a copper cylinder of solid copper, but there are other suitable materials which could include, for example, Aluminum, Brass, ceramics, thermal gels, etc.
It is therefore an object of the present invention to provide a cryosurgical device which includes a hand held applicator unit which is relatively lightweight, compact, and easily utilized, and which is sufficiently chilled so as to provide optimal cryosurgical applications.
It is another object of the present invention to provide a cryosurgical system comprising a thermo-cooling base unit configured to interface with and quickly and effectively super-cool a hand held cryogen applicator unit.
It is another object of the present invention to provide a cryosurgical system comprising a cryogen applicator unit comprising an insulated thermal mass having an exposed end configured to engage diverse application tips, said applicator unit having temperature indicator means.
It is another object of the present invention to provide a cryosurgical system comprising a thermo-cooling base unit comprising cascaded Rankine process refrigeration units configured to super-cool a cold plate, said cold plate having situated thereupon a thermoelectric device engaging at its cold side a socket configured to engage said exposed end of said cryogen applicator unit.
It is another object of the present invention to provide a cryosurgical system comprising a base thermo-cooling station for removably super-cooling a hand manipulable thermal mass, said base station including a socket for receiving an exposed end of said thermal mass, and means for providing liquid antifreeze in said socket so as to prevent any air gaps between said exposed end and said socket when engaged.
Lastly, it is an object of the present invention to provide a method and system for cryo-ablation of biological tissue utilizing a super-chilled, hand-held thermal mass and separate thermal cooling base station.